Aromatic polycarbonate and production process therefor

ABSTRACT

A polycarbonate having excellent color and stability and a production process therefor. 
     In the production of a polycarbonate by melt polycondensing a dihydroxy compound and a carbonic acid diester in the presence of an ester exchange catalyst, the each content of an aldehyde group in the dihydroxy compound and the carbonic acid diester is reduced to 3×10 −6  equivalent/mol or less.

FIELD OF THE INVENTION

The present invention relates to an aromatic polycarbonate and aproduction process therefor. More specifically, it relates to a processfor producing an aromatic polycarbonate from an aromatic dihydroxycompound and a carbonic acid diester, both having a low content of analdehyde compound, by an ester exchange method and to an aromaticpolycarbonate having excellent color and stability obtained by the aboveprocess.

PRIOR ART

Polycarbonates which are superior to other resins in moldability,mechanical strength and optical properties such as achromatictransparency are widely used as materials for transparent substrates forrecording media which record and/or reproduce information using laserlight, such as audio disks, laser disks, optical disk memories andmagneto-optic disks, as well as for transparent sheets and lenses.

The polycarbonates are produced from an aromatic dihydroxy compound anda carbonic bond forming precursor. As the production process thereof areknown an interfacial polycondensation process in which phosgene isdirectly reacted as the carbonate bond forming precursor and a meltpolycondensation process in which an ester exchange reaction between acarbonic acid diester and phosgene is carried out. The meltpolycondensation process has such an advantage that a polycarbonateresin can be produced at a lower cost than the interfacialpolycondensation process.

A polycarbonate produced by an ester exchange melt polycondensationprocess using a conventionally known ester exchange catalyst such as analkali metal salt catalyst, for example, sodium hydroxide is disclosedin “Plastic Material Course (17) Polycarbonate, Chapter 4, pp. 48-53”published by Nikkan Kogyo Shimbun Co., Ltd. Since this polycarbonate isobtained by polymerization by distilling off a monomer component such asa phenol, an aromatic dihydroxy compound or diphenyl carbonate at atemperature of 250° C. or more for 1 hour or more, undesired sidereactions such as branching or decomposition occur during thispolymerization. These undesired side reactions include a decarboxylationreaction and a Kolbe-Schmitt similar reaction described in “Chemistryand Physics of Poly-carbonates, pp. 47-48” written by H. Schnell andpublished by Interscience Publishers Co., Ltd. When these side reactionsoccur, color developing impurities or a branch structure are formed inthe obtained polycarbonate and the obtained polycarbonate is apt todeteriorate in color and to become inferior in heat resistance andhydrolysis resistance as it contains a hetero-bond component other thanits own carbonate bond in the molecule, or in homogeneity andtransparency as it contains a gelled substance.

Therefore, the application of a polycarbonate produced by the meltpolymerization process is restricted compared with a polycarbonateproduced by the interfacial polymerization process.

To solve the above problems, paying attention to metal impuritiescontained in a carbonic acid diester and/or an aromatic dihydroxycompound which are raw materials for the production of an aromaticpolycarbonate, there are proposed a method for reducing the content ofan element such as Na, Fe, Cr or Mn (refer to JP-A 5-148355 and JP-A6-32885) (the term “JP-A” as used herein means an “unexamined publishedJapanese patent application”) and a method for reducing the amount of aninorganic non-metal ion such as hydrolysable chlorine (JP-A-2-153927).

Meanwhile, as for organic impurities contained in the carbonic aciddieter and/or aromatic dihydroxy compound, it is well known that organicimpurities having a benzene ring are contained in the aromatic dihydroxycompound such as 2,2-bis(4-hydroxyphenyl)propane (to be referred to as“bisphenol A” hereinafter) as disclosed in “High Purification TechnologySystem, Vol. 3, High-purity Substance Production Process (published byFuji Technosystem), pp. 149-160, 1997” and documents cited in the abovedocument.

It is also known that a carbonate bond forming precursor, for example, acarbonic acid diester may contain an impurity having a salicylic acidstructure which is a product of a decomposition reaction similar to aKolbe-Schmitt reaction, or an impurity having a benzophenone skeleton.

It is also proposed to solve the above problems by controlling theamounts of organic impurities and the above metallic or inorganic ionicimpurities contained in bisphenol A or carbonic acid diester (EP-A872507 and JP-A 7-33866). However, it cannot be said that the obtainedpolycarbonate is satisfactory in terms of color and stability. That is,it cannot be said that problems with color and stability are completelysolved for industrial-scale production.

Further, as proposals aimed to solve these problems using an esterexchange catalyst, JP-A 4-89824 discloses a catalyst which comprises 1)a nitrogen-containing basic compound, alkali metal compound and boricacid or boric acid ester, JP-A 4-46928 discloses a catalyst whichcomprises an electron donating amine compound and alkali metal compound,and JP-A 4-175368 discloses a technology for adding an acidic compoundand epoxy compound to a polycarbonate produced by melt polycondensationin the presence of an alkali metal catalyst.

However, the problems with color and stability are not completely solvedby the above conventional methods such as control of the amounts ofimpurities or selection of the type of catalyst.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forproducing an aromatic polycarbonate which is excellent in color andstability by an ester exchange method.

It is another object of the present invention to provide a process forproducing an aromatic polycarbonate which is excellent in color andstability and has a low content of a hetero-bond such as a branchstructure.

It is still another object of the present invention to provide a processfor producing an aromatic polycarbonate which is particularly excellentin color with a conventionally unknown minus b value.

It is a further object of the present invention to provide an aromaticpolycarbonate which is excellent in both color and stability asdescribed above.

Other objects and advantages of the present invention will becomeobvious from the following description.

According to the present invention, firstly, the above objects andadvantages of the present invention are attained by a process forproducing a polycarbonate by melt polycondensing a dihydroxy compoundand a carbonic acid diester in the presence of an ester exchangecatalyst, wherein a raw material which contains a dihydroxy compoundrepresented by the following formula (1):

wherein R¹ and R² are each independently an alkyl group having 1 to 20carbon atoms, alkoxy group having 1 to 20 carbon atoms, cycloalkyl grouphaving 6 to 20 carbon atoms, aryl group having 6 to 20 carbon atoms,cycloalkoxy group having 6 to 20 carbon atoms or aryloxy group having 6to 20 carbon atoms, m and n are each independently an integer of 0 to 4,and X is a single bond, oxygen atom, carbonyl group, alkylene grouphaving 1 to 20 carbon atoms, alkylidene group having 2 to 20 carbonatoms, cycloalkylene group having 6 to 20 carbon atoms, cycloalkylidenegroup having 6 to 20 carbon atoms, arylene group having 6 to 20 carbonatoms or a group having 6 to 20 carbon atoms, and an aldehyde compoundin an amount of no more than 3×10⁻⁶ equivalent in terms of an aldehydegroup based on 1 mol of the dihydroxy compound represented by the aboveformula (1) is used as one raw material comprising the above dihydroxycompound and a raw material which contains a carbonic acid diester andan aldehyde compound in an amount of no more than 3×10⁻⁶ equivalent interms of an aldehyde group based on 1 mol of the carbonic acid diesteris used as the other raw material comprising the above carbonic aciddiester.

According to the present invention, secondly, the above objects andadvantages of the present invention are attained by an aromaticpolycarbonate pellet which comprises an aromatic polycarbonate composedmainly of a recurring unit represented by the following formula (2):

wherein R¹ and R² are each independently an alkyl group having 1 to 20carbon atoms, alkoxy group having 1 to 20 carbon atoms, cycloalkyl grouphaving 6 to 20 carbon atoms, aryl group having 6 to 20 carbon atoms,cycloalkoxy group having 6 to 20 carbon atoms or aryloxy group having 6to 20 carbon atoms, m and n are each independently an integer of 0 to 4,and X is a single bond, oxygen atom, carbonyl group, alkylene grouphaving 1 to 20 carbon atoms, alkylidene group having 2 to 20 carbonatoms, cycloalkylene group having 6 to 20 carbon atoms, cycloalkylidenegroup having 6 to 20 carbon atoms, arylene group having 6 to 20 carbonatoms or alkylene-arylene-alkylene group having 6 to 20 carbon atoms,and having a viscosity average molecular weight of 10,000 to 17,000 anda value of 1×10⁻⁶ to 20×10⁻⁶ obtained by dividing the average value ofabsorbance at a wavelength of 400 nm and absorbance at a wavelength of430 nm by absorbance at a wavelength of 260 nm, and which has a b valueof −1.0 to 0.0 measured in accordance with JIS K7105.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinbelow. A description isfirst given of the process of the present invention.

In the present invention, the one raw material comprising a dihydroxycompound contains a dihydroxy compound represented by the formula (1)and an aldehyde compound in an amount of no more than 3×10⁻⁶ equivalent,preferably no more than 2×10⁻⁶ equivalent, more preferably no more than1×10⁻⁶ equivalent in terms of an aldehyde group based on 1 mol of thedihydroxy compound represented by the formula (1). This raw materialhaving a low content of an aldehyde compound can be advantageouslyprepared by contact hydrogenating a raw material containing an aldehydecompound in an amount of more than 3×10⁻⁶ equivalent in terms of analdehyde group based on 1 mol of the dihydroxy compound represented bythe formula (1).

In the present invention, the other raw material comprising a carbonicacid diester contains a carbonic acid diester and an aldehyde compoundin an amount of no more than 3×10⁻⁶ equivalent, preferably no more than2×10⁻⁶ equivalent, more preferably no more than 1×10⁻⁶ equivalent interms of an aldehyde group based on 1 mol of the carbonic acid diester.The other raw material having a low content of an aldehyde compound canbe advantageously prepared by contact hydrogenating a raw materialcontaining an aldehyde compound in an amount of more than 3×10⁻⁶equivalent in terms of an aldehyde group based on 1 mol of the carbonicacid diester.

In the present invention, the total amount of aldehyde compoundscontained in the one raw material comprising a dihydroxy compound andthe other raw material comprising a carbonic acid diester is preferablyno more than 3×10⁻⁶ equivalent, more preferably no more than 2×10⁻⁶equivalent, particularly preferably 1×10⁻⁶ equivalent in terms of analdehyde group based on 1 mol of the dihydroxy compound represented bythe above formula (1).

A contact hydrogenation reaction for the one raw material comprising adihydroxy compound and the other raw material comprising a carbonic aciddiester can be carried out on a mixture of the both materials.

The contact hydrogenation reaction is preferably carried out in areaction solvent in the presence of a catalyst.

Preferred examples of the catalyst used for contact hydrogenationinclude conventionally known heterogeneous catalysts such aspalladium-carbon, platinum-carbon, palladium black and ruthenium-carbon.

The reaction solvent used at the time of contact hydrogenation ispreferably a lower alcohol in the case of the aromatic dihydroxycompound and an ether-based solvent in the case of the carbonic aciddiester. Illustrative examples of the lower alcohol include methanol,ethanol and isopropyl alcohol, and illustrative examples of theether-based solvent include tetrahydrofuran, dioxane and ethylene glycoldimethyl ether.

The content of the aldehyde group can be easily reduced to 3μ-equivalents or less based on 1 mol of the dihydroxy compound bycontact hydrogenation. Preferably, the solvent contains no aldehydecompound. Further, to control the total content of specific metalcomponents in the aromatic dihydroxy compound and the carbonic aciddiester to a low level, a solvent for application in the electronicindustry having a low total content of specific metal impurities is morepreferred.

The content of the aldehyde group is measured by a fluorescentderivation technique described in “BUNSEKI KAGAKU Vol. 34, pp. 314-318,1985”. The aldehyde group detection limit of the technique is 0.5×10⁻⁶equivalent/mol or less.

The above aldehyde compound include aliphatic aldehydes such asformaldehyde, acetaldehyde and hexylaldehyde, alicyclic aldehydes andaromatic aldehydes.

The aldehyde compound is often contained in the dihydroxy compound andthe carbonic acid diester as an impurity.

After contact hydrogenation, a conventionally known purification methodsuch as cleaning, recrystallization, crystallization, sublimationpurification or distillation is preferably carried out. A combinationthereof is particularly recommended.

In the present invention, the one raw material contains a carboxylicacid compound in an amount of preferably no more than 3×10⁻⁶ equivalent,more preferably no more than 2×10⁻⁶ equivalent, particularly preferablyno more than 1×10⁻⁶ equivalent in terms of a carboxyl group based on 1mol of the dihydroxy compound represented by the above formula (1).

The carboxylic acid compound includes lower carboxylic acids such asformic acid, acetic acid, propionic acid, oxalic acid, glycolic acid,malic acid, citric acid and tartaric acid. The content of the carboxylicacid compound which is the above upper limit or less can be attained bya purification method such as cleaning after the above contacthydrogenation.

Examples of the dihydroxy compound represented by the above formula (1)include BPA, bis(4-hydroxyphenyl)methane,bis(4-hydroxy-3,5-dimetylphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,1,1-bis(4-hydroxyphenyl)-1-phenylethane,1,1-bis(4-hydroxyphenyl)propane, 2,2-bis(2-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3-methylphenyl)propane,2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,2,2-bis(4-hydroxy-3,5-dibromophenyl)propane,2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3-methylphenyl)propane,2,2-bis(4-hydroxy-3-phenylphenyl)propane,2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)-3-methylbutane,2,2-bis(4-hydroxyphenyl)-3,3-dimethylbutane,2,4-bis(4-hydroxyphenyl)-2-methylbutane,2,2-bis(4-hydroxyphenyl)pentane,2,2-bis(4-hydroxyphenyl)-4-methylpentane,3,3-bis(4-hydroxyphenyl)pentane, 1,1-bis(4-hydroxyphenyl)cyclohexane,1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,9,9-bis(4-hydroxyphenyl)fluorene,9,9-bis(4-hydroxy-3-methylphenyl)fluorene, bis(4-hydroxyphenyl)sulfide,bis(4-hydroxyphenyl)sulfone, 4,4′-dihydroxydiphenyl sulfoxide,4,4′-dihydroxydiphenyl sulfide, 4,4′-dihydroxydiphenyl ketone,4,4′-dihydroxydiphenyl ether, hydroquinone, 2-t-butylhydroquinone,resorcin, 4,4′-dihydroxydiphenyl and those having an alkyl group or arylgroup as a substituent in the aromatic ring thereof. Out of these, BPAis particularly preferred from an economical point of view. They may beused alone or in combination of two or more.

The one raw material comprising a dihydroxy compound is used in the formof globular particles which include particles having a diameter of 0.1to 3 mm in an amount of 70 wt % or more and have a specific surface areaof 0.05 to 0.2m²/g and a pore volume of 0.01 to 0.1 ml/g. As forparticle size, particles having a diameter of 0.1 to 2 mm are containedin an amount of preferably 70 wt % or more, more preferably 80 wt % ormore, particularly preferably 90 wt % or more. Further, particles havinga diameter of 0.1 mm or less are contained in an amount of preferably 10wt % or less, more preferably 5 wt % or less, particularly preferably 3wt % or less.

The specific surface area measured by a BET method is preferably 0.05 to0.1 m²/g.

The pore volume measured by a mercury penetration method (obtained basedon the assumption that a peak at a radius of 100 nm to 600 μm isregarded as a particle pore distribution) is preferably 0.01 to 0.6ml/g, more preferably 0.01 to 0.4 ml/g, particularly preferably 0.01 to0.03 ml/g.

An aromatic polycarbonate which is excellent in color and transparencyand has small variations can be obtained by using the above one rawmaterial comprising a dihydroxy compound as globular particles havingthe above particle diameter distribution, specific surface area and poredistribution.

The L and b color values of the above globular particles are preferably80 or more and 2 or less, more preferably 83 or more and 1.5 or less,much more preferably 85 or more and 1 or less, particularly preferably85 or more and 0.5 or less, respectively.

The carbonic acid diester is a carbonic acid diester of an aryl grouphaving 6 to 10 carbon atoms, aralkyl group or alkyl group having 1 to 4carbon atoms, which may be substituted. Specific examples of thecarbonic acid diester include diphenyl carbonate, ditolyl carbonate,bis(chlorophenyl)carbonate, m-cresyl carbonate, bis(diphenyl)carbonate,diethyl carbonate and dibutyl carbonate. Out of these, diphenylcarbonate is preferred.

The above other raw material comprising a carbonic acid diesterpreferably has a small specific surface area and a small pore volumelike the above one raw material comprising a dihydroxy compound.However, as the carbonic acid diester has higher stability than thedihydroxy compound, the necessity of controlling the particle sizedistribution is smaller than the dihydroxy compound. Since the rawmaterial is often supplied as a solution, the necessity of taking intoconsideration the specific surface area and pore volume is small.

The reason why the above effect is developed when the dihydroxy compoundis prepared in the form of globular particles as described above isunknown but it is assumed that quality deteriorating factors are adheredto the surface of each particle and taken into the inside of each poreof the dihydroxy compound, thereby deteriorating the quality of thedihydroxy compound.

In the present invention, in consideration of influence on thedurability, color and transparency of a polycarbonate to be produced, itis recommended to use raw materials having a total content of tracemetal elements including transition metal elements such as Fe, Cr, Mn,Ni, Pb, Cu and Pd, metal and metalloid elements such as Al and Ti ofpreferably 50 ppb or less, more preferably 10 ppb or less, in additionto the controlled contents of the above aldehyde group and carboxylgroup as impurities.

To obtain an aromatic polycarbonate having higher durability, it ispreferred that the one raw material comprising a dihydroxy compound andthe other raw material comprising a carbonic acid diester should containan alkali metal element and/or an alkali earth metal element havinglarge ester exchange capability in an amount of only 60 ppb.

To obtain an aromatic polycarbonate having much higher durability, it ismore preferred that the content of an alkali metal element and/or analkali earth metal element in the aromatic dihydroxy compound andcarbonate bond forming precursor should be no more than 60 ppb and thatthe total content of transition metal elements in the above compound andthe precursor should be no more than 10 ppb.

Further, the total content of the above metals and metalloid elements inthe both raw materials is preferably no more than 20 ppb.

Although the total content of the transition metal elements, metals andmetalloid elements in the raw materials is preferably as small aspossible, the limits of the conventional technologies are more than 10ppb. An aromatic polycarbonate having excellent durability can beobtained by using a dihydroxy compound and a carbonic acid diesterhaving a total content of the above elements of no more than 10 ppb.

In the present invention, to obtain a raw material comprising adihydroxy compound which has a reduced total content of transitionmetal, metal and metalloid element impurities and a raw materialcomprising a carbonic acid diester which has also a reduced totalcontent of the above impurities, known purification methods such asdistillation, extraction, recrystallization and sublimation may beemployed. It is more preferred to combine the above purificationmethods.

To obtain a polycarbonate having a low total content of metal impuritiesin the present invention, a high-purity solvent having an extremely lowtotal content of metal impurities, for example, a solvent for use in theelectronic industry is preferably used for the purification of the rawmaterials.

In the process of the present invention, the above raw materials areused to produce a polycarbonate by melt polycondensing a dihydroxycompound and a carbonic acid diester in the presence of an esterexchange catalyst.

The ester exchange catalyst is preferably a combination of a) at leastone basic compound selected from the group consisting of anitrogen-containing basic compound and a phosphorus-containing basiccompound and b) at least one metal compound selected from the groupconsisting of an alkali metal compound and an alkali earth metalcompound.

The alkali metal compound or alkali earth metal compound is, forexample, a hydroxide, hydrocarbon compound, carbonate, carboxylate suchas acetate, stearate or benzoate, nitrate, nitrite, sulfite, cyanate,thiocyanate, borohydride, hydrogenphosphate, hypophosphite, bisphenol orphenol salt of an alkali metal or alkali earth metal.

Specific examples of the alkali metal compound and alkali earth metalcompound include sodium hydroxide, potassium bicarbonate, sodiumcarbonate, potassium carbonate, cesium carbonate, lithium acetate,rubidium nitrate, lithium nitrate, sodium nitrite, sodium sulfite,sodium cyanate, potassium cyanate, sodium thiocyanate, potassiumthiocyanate, cesium thiocyanate, sodium stearate, sodium borohydride,potassium borohydride, lithium borohydride, sodium phenylborate, sodiumbenzoate, disodium hydrogenphosphate, dipotassium hydrogenphosphate,lithium hypophosphite, sodium hypophosphite, potassium hypophosphite,rubidium hypophosphite, cesium hypophosphite, barium hypophosphite,cesium hypophosphite, disodium salts, monopotassium salts, sodiumpotassium salts of bisphenol A and potassium salts of phenol.

Out of these, the alkali metal compound is preferably a hypophisphite ofan alkali metal and the alkali earth metal compound is preferably ahypophosphite of an alkali earth metal.

The above metal compound is preferably used in an amount of 5×10⁻⁸ to5×10⁻⁶ equivalent based on 1 mol of the dihydroxy compound.

In the present invention, (a) an alkali metal salt of an ate complex ofa group XIV element of the periodic table or (b) an alkali metal salt ofan oxoacid of a group XIV element of the periodic table disclosed inJP-A 7-268091 may be used as the above alkali metal compound used as acatalyst. The group XIV element of the periodic table is silicon,germanium or tin.

By using the alkali metal compound as a polycondensation reactioncatalyst, a polycondensation reaction can proceed quickly andcompletely. Also, undesirable side reactions such as a branchingreaction which proceeds during a polycondensation reaction can besuppressed to a low level.

At least one compound selected from the group consisting of an oxoacidand oxide of a group XIV element of the periodic table and an alkoxideand phenoxide of the same element may be optionally used as a cocatalystin combination with the above catalyst in the polycondensation reactionof the present invention.

Undesirable phenomena such as a branching reaction liable to occurduring a polycondensation reaction, a main chain cleavage reaction andthe generation of foreign matter or burn mark in a molding apparatusduring molding can be effectively suppressed without ill-affecting theterminal blocking reaction and polycondensation reaction rate by usingthe cocatalyst in a specific ratio, which is preferred for the object ofthe present invention.

Examples of the oxoacid of the group XIV element of the periodic tableinclude silicic acid, stannic acid and germanic acid.

Examples of the oxide of the group XIV element of the periodic tableinclude silicon dioxide, tin dioxide, germanium dioxide, silicontetramethoxide, silicon tetraphenoxide, tetraethoxy tin, tetranonyloxytin, tetraphenoxy tin, tetrabutoxy germanium, tetraphenoxy germanium andcondensates thereof.

The cocatalyst is preferably used in an amount of 50 molar atoms or lessin terms of the group XIV element of the periodic table based on 1 molaratom-of the alkali metal element contained in the polycondensationreaction catalyst. When the cocatalyst is used in an amount of more than50 molar atoms in terms of the metal element, the polycondensationreaction rate slows down disadvantageously.

The cocatalyst is more preferably used in an amount of 0.1 to 30 molaratoms in terms of the group XIV element of the periodic table as thecocatalyst based on 1 molar atom of the alkali metal element containedin the polycondensation reaction catalyst.

As the catalyst are used a nitrogen-containing basic compound and aphosphorus-containing basic compound. These compounds may be used aloneor in combination of two or more.

Examples of the nitrogen-containing basic compound include ammoniumhydroxides having an alkyl, aryl or alkylaryl group such astetramethylammonium hydroxide, tetrabutylammonium hydroxide andbenzyltrimethylammonium hydroxide; basic ammonium salts having an alkyl,aryl or alkylaryl group such as tetramethylammonium acetate,tetraethylammonium phenoxide, tetrabutylammonium carbonates andbenzyltrimethylammonium benzoates; tertiary amines such as triethylamineand dimethylbenzylamine; and basic salts such as tetramethylammoniumborohydride, tetrabutylammonium borohydride and tetramethylammoniumtetraphenylborate.

Examples of the phosphorus-containing basic compound include phosphoniumhydroxides having an alkyl, aryl or alkylaryl group such astetrabutylphosphonium hydroxide and benzyltrimethylphosphoniumhydroxide; and basic salts such as tetramethylphosphonium borohydride,tetrabutylphosphonium borohydride and tetramethylphosphoniumtetraphenylborate.

The above nitrogen-containing basic compound or phosphorus-containingbasic compound is preferably used in an amount of 1×10⁻⁵ to 1×10⁻³equivalent in terms of the basic nitrogen atom or basic phosphorus atombased on 1 mol of the dihydroxy compound. The amount is more preferably2×10⁻⁵ to 5×10⁻⁴ equivalent, particularly preferably 5×10⁻⁵ to 5×10⁻⁴equivalent based on the same standard.

It has been found that in order to improve the color of the obtainedpolycarbonate at this point, use of the nitrogen-containing basiccompound or phosphorus-containing basic compound in such an amount thatit does not exceed 20×Fe*)+200 μ-equivalent (Fe* (wtppb): the totalcontent of iron contained in the dihydroxy compound and the carbonicacid diester as raw materials) is particularly effective. The amount isparticularly preferably such that it does not exceed 20×(Fe*)+150.

Although the reason is not made clear, it is presumed that the color ofa polycarbonate is worsened by interaction between iron contained in thenitrogen-containing basic compound or phosphorus-containing basiccompound as a raw material and the nitrogen-containing basic compoundand/or phosphorus-containing basic compound. From this point of view, itis preferred to reduce the total content of metal impurities as much aspossible.

The melt polymerization process is carried out by stirring a dihydroxycompound and a carbonic acid diester under normal pressure and/or avacuum nitrogen atmosphere while they are heated and distilling off theformed alcohol or phenol. The reaction temperature, which differsaccording to the boiling point of the formed product or the like, isgenerally 120 to 350° C. to remove the alcohol or phenol formed by thereaction.

The formed alcohol or phenol is easily distilled off by placing thesystem under vacuum in the latter stage of the reaction. The insidepressure of the system in the latter stage of the reaction is preferably133.3 Pa (1 mmHg) or less, more preferably 66.7 Pa (0.5 mmHg) or less.

In melt polymerization, another copolymerizable compound given below maybe optionally incorporated in the main chain of a polycarbonate inaddition to the above dihydroxy compound (aromatic dihydroxy compound)and carbonic acid diester.

Examples of the copolymerizable compound include aliphatic and alicyclicdiols and polyols such as ethylene glycol, 1,4-butanediol, polyethyleneglycol, 1,4-cyclohexane dimethanol,3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane,tricyclo(5.2.1.0^(2,6))decanedimethanol, trimethylolpropane andpentaerythritol; aromatic polyhydroxy compounds such as1,1,1-tris(4-hydroxyphenyl)ethane and1,1,2,2-tetrakis(3-methy-4-hydroxyphenyl)ethane; aliphatic and aromaticoxycarboxylic acids such as lactic acid, parahydroxybenzoic acid and6-hydroxy-2-naphthoic acid; dicarboxylic acids such as succinic acid,fumaric acid, adipic acid, dodecane diacid, terephthalic acid,2,6-naphthalenedicarboxylic acid, pyromellitic acid and trimelliticacid; and polycarboxylic acids.

To produce a polycarbonate by carrying out a reaction by meltpolycondensation, a terminal capping agent and an antioxidant agent suchas steric hindrance phenol may be used as required. The polycarbonate ofthe present invention includes branched polycarbonates prepared bycopolymerizing a polyfunctional aromatic compound having a functionalityof 3 or more and polyester carbonates prepared by copolymerizing anaromatic or aliphatic bifunctional carboxylic acid. Two or more of theobtained polycarbonates may be mixed together.

The molecular weight of the polycarbonate is preferably 10,000 to22,000, more preferably 12,000 to 20,000, particularly preferably 13,000to 18,000 in terms of viscosity average molecular weight (M) as asubstrate material. A polycarbonate having the above viscosity averagemolecular weight has sufficiently high strength as an optical materialand excellent melt fluidity at the time of molding and is therefore freefrom molding strain. For transparent applications such as sheets, theviscosity average molecular weight of the polycarbonate is preferablyselected from a range of 17,000 to 100,000, more preferably from a rangeof 20,000 to 80,000.

According to the present invention, as a polycarbonate particularlysuitable for the production of an optical disk substrate, there isprovided an aromatic polycarbonate pellet which comprises an aromaticpolycarbonate composed mainly of a recurring unit represented by thefollowing formula (2):

wherein R¹ and R²are each independently an alkyl group having 1 to 20carbon atoms, alkoxy group having 1 to 20 carbon atoms, cycloalkyl grouphaving 6 to 20 carbon atoms, aryl group having 6 to 20 carbon atoms,cycloalkoxy group having 6 to 20 carbon atoms or aryloxy group having 6to 20 carbon atoms, m and n are each independently an integer of 0 to 4,and X is a single bond, oxygen atom, carbonyl group, alkylene grouphaving 1 to 20 carbon atoms, alkylidene group having 2 to 20 carbonatoms, cycloalkylene group having 6 to 20 carbon atoms, cycloalkylidenegroup having 6 to 20 carbon atoms, arylene group having 6 to 20 carbonatoms or alkylene-arylene-alkylene group having 6 to 20 carbon atoms,and having a viscosity average molecular weight of 10,000 to 17,000 anda value of 1×10⁻⁶ to 20×10⁻⁶ obtained by dividing the average value ofabsorbance at a wavelength of 400 nm and absorbance at a wavelength of430 nm by absorbance at a wavelength of 260 nm, and which has a b valueof −1.0 to 0.0, preferably −0.5 to 0.0 measured in accordance with JISK7105.

In the present invention, to obtain an aromatic polycarbonate whichhardly experiences a reduction in molecular weight and discoloration,attention is paid to the viscosity stability of a molten polymer. Themelt viscosity stability is evaluated by the absolute value of a changein melt viscosity measured at a shear rate of 1 rad/sec in a stream ofnitrogen at 300° C. for 30 minutes and expressed by a change rate perminute. This value is preferably 0.5% or less. When this value is large,the deterioration of the polycarbonate by hydrolysis may be promoted.The present inventor judges that this value should be set to 0.5% toensure the practical level of stability to hydrolysis. To this end, themelt viscosity is preferably stabilized by using a melt viscositystabilizer after polymerization.

The melt viscosity stabilizer in the present invention also has thefunction of deactivating part or all of the activity of a polymerizationcatalyst used for the production of a polycarbonate.

As for the addition of the melt viscosity stabilizer, for example, itmay be added while the polymer is molten after polymerization or afterthe polycarbonate is pelletized and re-molten. In the former case, themelt viscosity stabilizer may be added while the polycarbonate which isthe reaction product in the reactor or extruder is molten, or may beadded and kneaded while the polycarbonate obtained after polymerizationis pelletized from the reactor through the extruder.

Any known melt viscosity stabilizer may be used. From the viewpoint ofthe large effect of improving the color and physical properties such asheat resistance and boiling water resistance of the obtained polymer,sulfonic acid compounds such as organic sulfonic acid salts, organicsulfonic acid esters, organic sulfonic anhydrides and organic sulfonicacid betain may be used, and phosphonium salts of sulfonic acid and/orammonium salts of sulfonic acid are preferably used. Out of these,dodecylbenzenesulfonic acid tetrabutyl phosphonium salts andparatoluenesulfonic acid tetrabutyl ammonium salts are particularlypreferred.

The above aromatic polycarbonate has an aryloxy group and a phenolichydroxyl group as the main terminal groups and the concentration of thephenolic hydroxyl group is preferably 60 mol % or less, more preferably40 mol % or less, particularly preferably 30 mol % or less. When thephenolic terminal group is contained in the above weight ratio, theobject of the present invention can be more advantageously attained andthe moldability of the composition (mold staining properties,releasability; to be simply referred to as “moldability” hereinafter) isalso improved.

The aryloxy group is preferably a phenyloxy group having a hydrocarbongroup having 1 to 20 carbon atoms as a substituent, or nonsubstitutedphenyloxy group. From the viewpoint of resin heat stability, a phenyloxygroup having a tertiary alkyl group, tertiary aralkyl group or arylgroup as a substituent, or nonsubstituted phenyloxy group is preferred.

Preferred examples of the aryloxy group include phenoxy group,4-t-butylphenyloxy group, 4-t-amylphenyloxy group, 4-phenylphenyloxygroup and 4-cumylphenyloxy group.

In the interfacial polymerization process, the concentration of theterminal phenolic hydroxyl group can be reduced to a low level by meansof a molecular weight modifier. However, in the melt polymerizationprocess, the concentration of the terminal hydroxyl group must bereduced positively because an aromatic polycarbonate containing aterminal phenolic hydroxyl group in an amount of generally 50 mol %,sometimes 60 mol % or more is readily produced through a chemicalreaction.

That is, the following conventionally known method 1) or 2) can beadvantageously used to adjust the concentration of the terminal hydroxylgroup to the above range:

1) method of controlling the molar ratio of charge stocks; The molarratio of the carbonic acid diester to the dihydroxy compound at the timeof charging for a polymerization reaction is increased to a range of1.01 to 1.10 in consideration of the characteristic features of apolymerization reactor.

2) terminal capping method; At the end of a polymerization reaction, theterminal hydroxyl groups are capped by adding a salicylate-basedcompound described in USP 5696222 in accordance with the methoddisclosed by the above document.

When the salicylate-based compound is used to cap the terminal hydroxylgroups, the amount of the salicylate-based compound is preferably 0.8 to10 mols, more preferably 0.8 to 5 mols, particularly preferably 0.9 to 2mols based on 1 chemical equivalent of the terminal hydroxyl groupbefore a capping reaction. By adding the salicylate-based compound inthe above weight ratio, 80% or more of the terminal hydroxyl groups canbe capped advantageously. To carry out this capping reaction, catalystsdisclosed by the above US patent are preferably used.

The concentration of the terminal hydroxyl group is preferably reducedbefore the deactivation of a polymerization catalyst.

Salicylate-based compounds enumerated in the specification of U.S. Pat.No. 5,696,222 may be preferably used as the salicylate-based compound,as exemplified by 2-methoxycarbonylphenylaryl carbonates such as2-methoxycarbonylphenyl-phenyl carbonate; 2-methoxycarbonylphenyl-alkylcarbonates such as 2-methoxycarbonylphenyl-lauryl carbonate;2-ethoxycarbonylphenyl-aryl carbonates such as2-ethoxycarbonylphenyl-phenyl carbonate; 2-ethoxycarbonylphenyl-alkylcarbonates such as 2-ethoxycarbonylphenyl-octyl carbonate;(2′-methoxycarbonylphenyl)esters of aromatic carboxylic acids such as(2-methoxycarbonylphenyl)benzoate; and aliphatic carboxylates such as(2-methoxycarbonylphenyl)stearate andbis(2-methoxycarbonylphenyl)adipate.

An aromatic polycarbonate is obtained by the above process. When moldedarticles are formed from the aromatic polycarbonate, a conventionallyknown processing stabilizer, heat stabilizer, antioxidant, ultravioletlight absorber, antistatic agent, flame retardant and release agent maybe added according to application purpose.

For example, various stabilizers may be blended to prevent a reductionin molecular weight and deterioration in color of an aromaticpolycarbonate. Examples of the heat stabilizer include hypophosphorousacid, phosphorous acid, phosphoric acid, phosphonous acid, phosphonicacid, salts and esters thereof, steric hindrance amine antioxidants,steric hindrance phenolic antioxidants and carbon radical scavengers.Trisnonylphenyl phosphate, tris(2,4-di-t-butylphenyl)phosphite,tetrabutylphosphonium dihydrogenphosphates,tetrakis(2,4-di-t-butylphenyl) 4,4′-biphenylenediphosphinate,trimethylphosphate, dimethyl benzenephosphonate,5,7-di-t-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one, n-octadecyl3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylateare preferably used. These heat stabilizers may be used alone or incombination of two or more. The amount of the heat stabilizer ispreferably 0.0001 to 1 part by weight, more preferably 0.0002 to 0.5part by weight, particularly preferably 0.0005 to 0.1 part by weightbased on 100 parts by weight of the aromatic polycarbonate.

The aromatic polycarbonate may be mixed with a release agent to furtherimprove releasability from a mold at the time of melt molding. Examplesof the release agent include olefin-based wax, olefin-based waxcontaining a carboxyl group and/or carboxylic acid anhydride group,silicone oil, organopolysiloxane, higher fatty acid ester of amonohydric or polyhydric alcohol, paraffin wax and beeswax. The amountof the release agent is preferably 0.01 to 5 parts by weight based on100 parts by weight of the aromatic polycarbonate.

The higher fatty acid ester is preferably a partial ester or whole esterof a monohydric or polyhydric alcohol having 1 to 20 carbon atoms and asaturated fatty acid having 10 to 30 carbon atoms. The partial ester orwhole ester of a monohydric or polyhydric alcohol and a saturated fattyacid is preferably monoglyceride stearate, triglyceride stearate orpentaerythritol tetrastearate. The amount of the release agent ispreferably 0.01 to 5 parts by weight based on 100 parts by weight of thearomatic polycarbonate.

The aromatic polycarbonate may be mixed with inorganic and organicfillers to improve its stiffness. Examples of the inorganic fillerinclude lamellar or granular inorganic fillers such as talc, mica, glassflake, glass bead, calcium carbonate and titanium oxide, and fibrousfillers such as glass fiber, glass milled fiber, wollastonite, carbonfiber, aramide fiber and metal-based conductive fiber, and examples ofthe organic filler include organic particles such as crosslinked acrylparticle and crosslinked silicone particle. The total amount of theinorganic and organic fillers is preferably 1 to 150 parts by weight,more preferably 3 to 100 parts by weight based on 100 parts by weight ofthe aromatic polycarbonate.

The above inorganic fillers usable in the present invention may besurface treated with a silane coupling agent. A favorable effect such asthe suppression of the decomposition of the aromatic polycarbonate isobtained from this surface treatment.

The aromatic polycarbonate may further be blended with another resin.

Examples of the another resin include polyamide resins, polyimideresins, polyether imide resins, polyurethane resins, polyphenylene etherresins, polyphenylene sulfide resins, polysulfone resins, polyolefinresins such as polyethylene and polypropylene, polyester resins such aspolyethylene terephthalate and polybutylene terephthalate, amorphouspolyarylate resins, polystyrene resins, acrylonitrile/styrene copolymer(AS resin), acrylonitrile/butadiene/styrene copolymer (ABS resin),polymethacrylate resins, phenol resins and epoxy resins.

The aromatic polycarbonate obtained in the present invention has theeffect of retaining color and durability, particularly durability for along time under extreme temperature and humidity conditions. Substrates,obtained from the polymer, for high-density optical disks typified byCD, CD-ROM, CD-R, CD-RW, magnetic optical disks (MO) and disk versatiledisks (such as DVD-ROM, DVD-Video, DVD-Audio, DVD-R and DVD-RAM) canretain high reliability for a long time. The aromatic polycarbonate isparticularly useful for high-density optical disks such as digitalversatile disks.

Sheets formed from the aromatic polycarbonate produced in the presentinvention are excellent in adhesion and printability and widely used inelectric parts, building material parts and auto parts thanks to theabove characteristic properties. More specifically, they are useful foroptical applications such as various window materials, that is, grazingproducts for window materials for general houses, gyms, baseball domesand vehicles (such as construction machinery, automobiles, buses, bullettrains and electric vehicles), various side wall panels (such as skydomes, top lights, arcades, wainscots for condominiums and side panelson roads), window materials for vehicles, displays and touch panels forOA equipment, membrane switches, photo covers, polycarbonate resinlaminate panels for water tanks, front panels and Fresnel lenses forprojection TVs and plasma displays, optical cards, liquid crystal cellsconsisting of an optical disk and a polarizer, and phase differencecompensators. The thickness of the sheet does not need to beparticularly limited but it is generally 0.1 to 10 mm, preferably 0.2 to8 mm, particularly preferably 0.2 to 3 mm. Various treatments forproviding new functions (such as a laminate treatment for improvingweatherability, a treatment for improving scratch resistance to improvesurface hardness, surface drawing and processing for making translucentor opaque) may be carried out on the aromatic polycarbonate sheet.

To mix the above components with the aromatic polycarbonate, any meansis employed. For example, a tumbler, twin-cylinder mixer, super mixer,Nauter mixer, Banbury mixer, kneading roll or extruder is advantageouslyused. The thus obtained aromatic polycarbonate resin composition is meltextruded to form a sheet directly or after it is pelletized by a meltextruder.

In an extrusion step (pelletizing step) for obtaining palletizingpolycarbonate resin to be injection molded, foreign matter is preferablyremoved by passing the polycarbonate through a sintered metal filterhaving a filtration accuracy of 10 μm while it is molten. An additivesuch as a phosphorus-based antioxidant is preferably added as required.Anyway, it is desired to reduce the contents of foreign matter,impurities and solvent in the raw material resin as much as possiblebefore injection molding.

To produce an optical disk substrate from the above polycarbonate resin,an injection molding machine (including an injection compression moldingmachine) is used. This injection molding machine may be a generally usedinjection molding machine but preferably an injection molding machinewhose cylinders and screws are made from a material having low adhesionto a resin and corrosion resistance and wearing properties in order tosuppress the formation of a carbide and improve the reliability of adisk substrate. The preferred injection molding conditions include acylinder temperature of 300 to 400° C. and a mold temperature of 50 to140° C., thereby making it possible to obtain an optical disk substratehaving excellent optical properties. The molding environment ispreferably as clean as possible in consideration of the object of thepresent invention. It is also important that the material to be moldedshould be completely dried to remove its water and that retention whichcauses the decomposition of a molten resin should be prevented.

The aromatic polycarbonate produced in the present invention may be usedfor any purpose, for example, electronic and communication equipment, OAequipment, optical parts such as lenses, prisms, optical disk substratesand optical fibers, electronic and electric appliances such as homeelectric appliances, lighting members and heavy electric members,mechanical materials such as car interior and exterior parts, precisionmachines and insulating materials, miscellaneous materials such asmedical materials, safety and protective materials, sports and leisureoutfits, and home supplies, container and package materials, and displayand decoration materials. They may also be advantageously used as acomposite material with another resin, or organic or inorganic material.

EXAMPLES

The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting.

“Parts” in the examples means “parts by weight”.

Analytical Method

Methods for testing aromatic polycarbonates produced in Examples andComparative Examples are given below.

1) viscosity average molecular weight (Mw): The viscosity of a solutionof 350 mg of a sample dissolved in 50 ml of methylene chloride wasmeasured with an Ubbellohde viscometer at 20° C. to obtain an intrinsicviscosity ([η]) and the viscosity average molecular weight was obtainedfrom this intrinsic viscosity according to the following expression.

[η]=1.23×10⁻⁴×Mw^(0.83)

2) method of measuring the total content of metal impurities device;ICP-MS SPQ 9000 of Seiko Instruments Co., Ltd. sample concentration; 0.5g of a sample was dissolved in 25 g of high-purity isopropyl alcohol foruse in the electronic industry and measured to determine the totalcontent of metal impurities from a standard sample calibration curve.

3) melt viscosity stability

The absolute value of a change in melt viscosity was measured at a shearrate of 1 rad/sec and a temperature of 300° C. in a stream of nitrogenwith the RAA type fluidity analyzer of Rheometrics Co., Ltd. for 30minutes to obtain a change rate per minute as melt viscosity stability.This value does not exceed 0.5% when the aromatic polycarbonate isstable for a long time.

4) determination of the amount of aldehyde

This was measured by the high-speed liquid chromatography of analiphatic aldehyde using fluorescent derivation withcyclohexane-1,3-dione (to be abbreviated as DHA hereinafter) inaccordance with a method described in BUNSEKI KAGAKU Vol. 34, pp. 314 to318. A predetermine amount of a derivative of acetaldehyde and DHA wasused as a reference material for the determination of the amount of theformed aldehyde.

Thereafter, about 0.1 g of a sample was weighed, and 2 ml of a DHAderivation reagent solution described in the above document was added tothe sample and reacted at 60° C. for 30 minutes to change aldehydescontained in the sample to DHA derivatives. The 440 nm fluorescentintensity of the sample was compared with the 440 nm fluorescentintensity. of the reference material, and all the aldehydes contained inthe sample were regarded as acetaldehyde and determined quantitativelyas the amount of an aldehyde functional group (equivalent/1 mol ofdihydroxy compound or 1 mol of carbonic acid diester compound).

The detection of an aldehyde by this method is possible even when theamount of an aldehyde functional group is 0.03 ppm as described in theanalytical example of the above document.

5) determination of the content of carboxyl group: measured by ionchromatography

About 5 g of a sample was weighed and placed in a polyethylene containerwith a cover, 20 ml of pure water was added, the container was covered,and extraction was carried out at 80° C. for 16 hours. Then, the extractwas treated with ultrasonic waves for 30 minutes and filtered with a0.45 μm membrane filter for ion chromatography to obtain a measurementsolution. This solution was analyzed by ion chromatography.

The analytical value of a solution which did not contain the sample andwas subjected to the same treatment as above was taken as a blank value.

Measurement Conditions

Column: IonpacAG4A-SC/AS4A-SC

Elute: 1.80 mM Na₂CO₃+1.70 mM NaHCO₃

Regenerated solution: 0.025N H₂SO₄

Detector: electric conductivity

Flow rate: 1.5 ml/min

Suppressor: micro-membrane suppressor

6) measurement of color; L and b values

A) polymer pellet:

Polymer pellets having a weight of 10 to 100 mg/pellet were measuredwith the Z-1001 DP color difference meter of Nippon Denshoku Co., Ltd.in accordance with JIS K7105.

B) color of bisphenol A prill:

Measured with the Z-1001 DP color difference meter of Nippon DenshokuCo., Ltd. like the polymer pellet.

7) color durability of polymer pellet

To test the durability of a polycarbonate under extreme temperature andhumidity conditions, a sample obtained by dividing the abovepolycarbonate pellet into 10 pieces was held in a thermo-hygrostat at atemperature of 80° C. and a relative humidity of 85% for 1,000 hours tomeasure the color b value of the polymer.

The absolute values of differences between the maximum values and theminimum values of 10 polymer samples after the durability test weretaken as ΔbMax-Min which is a polymer color variation.

The color stability Δb was obtained from the absolute value ofdifference in color b value before and after the durability test.

As these values are smaller, the color durability of a polymer pelletbecomes higher. When these values were 0.5 or less, it was judged thatthe polymer had desirable color durability even when it was used underextreme temperature and humidity conditions for a long time. A polymerhaving values larger than 1 was evaluated as unfavorable.

8) determination of concentration (mol %) of phenolic OH terminal group,number (equivalent/ton-PC) of phenolic OH terminal groups, concentration(mol %) of aryloxy terminal group, number (equivalent/ton-PC) of aryloxyterminal groups

About 0.02 g of a polymer sample was dissolved in 0.4 ml of heavychloroform and the concentration (mol %) of the phenolic OH terminalgroup based on the total of all the terminal groups and the number(equivalent/ton-PC) of phenolic OH terminal groups were measured by a¹H-NMR measuring instrument (EX-270 of JEOL Ltd.) at 20° C.

The concentration (mol %) of the aryloxy terminal group was obtainedfrom the concentration (mol %) of the 100-phenolic OH terminal group andthe number (equivalent/ton-PC) of aryloxy terminal groups was calculatedas a difference between the total number of all the terminal groupsobtained from the following equation and the number of phenolic OHterminal groups.

total number of all terminal groups(equivalent/ton-PC)=56.54/[η]^(1.4338)

9) amount of side-reaction of polymer

It was judged that a peak other than the peak of a polycarbonate seen atδ of 0 to 10 by ¹H-NMR measurement was derived from a side-reactionproduct such as a decomposed product or branched product which wasformed during polymerization. The ratio of an integrated value of 1,024peak intensities to the peak intensity of a polycarbonate methyl groupwas measured and when this value was 1.0×10⁻² or more, it was judgedthat the amount of a side-reaction of polymer was large.

10) purification examples of raw materials

a) Purification of bisphenol A (may be abbreviated as BPA hereinafter)

a)-1 Commercially available bisphenol A (before purification; GB) wasfed to a pressure vessel equipped with a decompressor and cooler andpurified by sublimation at a pressure of 13.3 Pa (0.1 Torr) or less anda temperature of 140° C. under a nitrogen atmosphere.

The sublimation purification was repeated three times to obtain purifiedbisphenol A (cB) and the sublimation purification was repeated fourtimes to obtain purified bisphenol A (dB).

a)-2 hydrogenation

100 parts by weight of the above purified bisphenol A (cB) was dissolvedin 1,000 parts by weight of high-purity methanol for use in theelectronic industry, the resulting solution was fed to an autoclaveequipped with a stirrer, and 1 part by weight of 1 wt % of a palladiumcarried on activated carbon was fed to the autoclave as a hydrogenationcatalyst to carry out a reaction at a hydrogen pressure of 1.0 atm (0.1MPa) and a temperature of 50° C. for 5 hours. After the reaction, thecatalyst was separated and the solvent was removed under vacuum toobtain purified bisphenol A (eB).

This purified bisphenol A (eB) was purified by sublimation under theabove conditions to obtain purified bisphenol A (fB).

The purities of the raw and purified bisphenol A are shown in Table 1.

TABLE 1 BPA impurities carboxylic aldehyde acid μ-equivalent/μ-equivalent/ metal impurities (ppb) Type of BPA symbol 1-mol of BPA1-mol of BPA Na Fe Cr Mn Ni Pb Cu Zn Pd In Si Al Ti raw BPA GB 12 8 8660 5 4 8 5 1* 11 1* 7 25 22 1* 3 times of purification cB  7 6  5 15 1*1* 1* 1* 1*  1* 1* 1*  2  1* 1* by sublimation 4 times of purificationdB  5 6  5  8 1* 1* 1* 1* 1*  1* 1* 1*  1*  1* 1* by sublimation cB +hydrogenation eB 1 or less 3  7 10 1* 1* 1* 1* 1*  1* 1* 1*  1*  1* 1*eB + sublimation fB 1 or less 2  6  8 1* 1* 1* 1* 1*  1* 1* 1*  1  1 1*(hydrogenation) 1*: 1ppb or less

a)-3 treatment of bisphenol A with hypophosphorous acid derivative

100 parts by weight of purified bisphenol A (fB) was immersed in 2,000parts by weight of a 3 wt % aqueous solution of hypophosphorous acid ora 1 wt % aqueous solution of sodium hypophosphite at 25° C. for 10hours. Bisphenol A was separated and washed with 2,000 parts by weightof distilled water at 98° C. under a nitrogen gas atmosphere for 5hours. The obtained bisphenol A was washed five times in total andvacuum dried to obtain purified bisphenol A (fB*) and purified bisphenolA (fB**).

b) purification of diphenyl carbonate (may be abbreviated as DPChereinafter)

b)-1 Distilled DPC was obtained by cleaning raw DPC (GD) with hot water(50° C.) three times, drying and carrying out vacuum distillation at 167to 168° C. and 2.00 kPa (15 mmHg) in accordance with the methoddescribed in “Plastic Material Lecture 17 Polycarbonate, pp. 45” writtenby Toshihisa Tachikawa and published by Nikkan Kogyo Shinbun Co., Ltd.to collect a fraction. The obtained distilled DPC was fed to a pressurevessel equipped with a decompressor and cooler to carry out sublimationpurification once at 13.3 Pa (0.1 Torr) or less and 80° C. under anitrogen atmosphere to obtain purified DPC (bD).

b)-2 hydrogenation

100 parts by weight of the distilled DPC was dissolved in 500 parts byweight of high-purity tetrahydrofuran for use in the electronicindustry, the resulting solution was fed to an autoclave equipped with astirrer, and 1 part by weight of 1 wt % of a palladium carried onactivated carbon was fed as a hydrogenation catalyst to carry out areaction at a hydrogen pressure of 1.0 atm (0.1 MPa) and a temperatureof 50° C. for 5 hours. The catalyst was separated after the reaction andthe solvent was removed under vacuum to collect DPC. The obtained DPCwas further purified by sublimation one more time as described above toobtain purified DPC (cD).

The purities of the raw and purified DPC are shown in Table 2.

TABLE 2 DPC impurities carboxylic aldehyde acid μ-equivalent/μ-equivalent/ metal impurities (ppb) Type of DPC symbol 1-mol of BPA1-mol of BPA Na Fe Cr Mn Ni Pb Cu Zn Pd In Si Al Ti raw DPC GD 7 5 96 4015 5 5 1 1* 11 1* 15 15 42 3* Washing with water/ bD 4 3 10  9  1* 1* 1*1* 1*  1* 1*  1*  2  1* 1* distillation/ sublimation × one timeHydrogenated DPC (bD) cD 1 or less 1 or less 10  9  1* 1* 1* 1* 1*  1*1*  1*  2  1 1* 1*: 1ppb or less

11) molding of bisphenol A prill

a) Purified bisphenol A (fB) was molten by heating at 170° C. under anitrogen atmosphere and flown and dropped from a nozzle having a radiusof 0.3 mm to form droplets which were then contacted to 77K coolingnitrogen gas countercurrently to be cooled at a rate of 100° C./sec ormore. Prills as large as 0.2 mm or less and 3 mm or more were removed byscreening to obtain prills having an average particle diameter of 1.5 mm(fB-a).

b) Molten bisphenol A (fB) was flown and dropped from a nozzle having aradius of 0.5 mm in place of the above nozzle having a radius of 0.3 mmto form droplets which were then contacted to 77K cooling nitrogen gascountercurrently to be cooled at a rate of 100° C./sec or more. Prillshaving a diameter of 0.2 mm or less and 3 mm or more were removed byscreening to obtain prills having an average particle diameter of 1.5 mm(fB-b).

c) Cooling was carried out at a rate of 100° C./sec or less in the samemanner as the prills (fB-b) except that droplets were contacted to 0° C.cooling nitrogen countercurrently and prills having a diameter of 0.2 mmor less and 3 mm or more were removed by screening to obtain prillshaving an average particle diameter of 1.5 mm (fB-c). The results areshown in Table 3.

12) specific surface area (m²/g)

This was measured by a BET specific surface area measuring method.

Device: BELSORP 36 high-accuracy fully automatic gas adsorber of NipponBell Co., Ltd.

Adsorption gas: Kr

Dead volume: He

Adsorption temperature: liquid nitrogen temperature (77K)

Pre-treatment before measurement: 50° C., vacuum deaeration (ultimatevacuum degree: up to 1 Pa)

Measurement mode: adsorption at isotherm

Measurement range: relative pressure (P/PO)=0.01 to 0.4

Equilibrium time=180 sec at each relative pressure

Measurement: About 0.2 to 0.5 g of a sample was weighed by the AEL200electronic balance of Shimadzu Corporation, enclosed in a sample tubeand measured, BET theory was applied, and analysis was made at arelative pressure (P/P0) of 0.05 to 0.30 where the theory was valid anda BET plot became a straight line to calculate specific surfacearea(m²/g). The results are shown in Table 3.

13) pore volume (ml/g)

9320 pore sizer of Micromeritecs Co., Ltd.

measurement pressure: 0.37 kPa to 207 MPa (pore diameter of 7 nm to 400μm)

measurement mode: pressure rise within the above pressure range

cell volume: 5 cm³

number of measurement times: 1 and 2

measurement: 0.2 to 1.2 g of a sample was weighed and placed in a cell,and mercury was injected into the cell under reduced pressure to obtainpore volume at a pore radius of 100 nm to 6 μm in consideration of thedeformation of sample particles and the interval between particles. Theresults are shown in Table 3.

TABLE 3 average specific surface particle wt % of particles surface areaof type of prill forming diame- having a size of area pore color BPAprill raw BPA conditions ter mm 0.1 to 3 mm m²/g ml/g L value b valueGB-0 Commercially GB 2.7  97 0.25 0.14 81 2.1 available BPA fB-aPurified BPA fB (a) 1.5 100 0.09 0.03 87 0.1 fB-b (b) 2.2 100 0.12 0.0587 0.5 fB-c (c) 2.3 100 0.21 0.11 86 1.5 fB-0 (fB) no conditions powder70 wt % or less 0.23 0.12 78 1.4

14) spectral stability

Measurement of Ultraviolet/visible Light Absorption Spectrum

measurement device: UV-2400PC of Shimadzu Corporation

measurement cell: quartz cell having an optical path length (1) of 1 cm

measurement: About 0.73 g of a polycarbonate was weighed and dissolvedin 10 ml of methylene chloride (sample A).

A solution (sample B) was prepared by diluting the sample A withmethylene chloride in a ratio of 1/10 and a sample (sample C) wasprepared by diluting the sample A with methylene chloride in a ratio of1/100.

Reference: solvent (methylene chloride)

The absorbance (A) was measured at a wavelength of 290 to 500 nm for thesample A, 275 to 275 nm for the sample B and 200 to 300 nm for thesample C and the absorption coefficient (E) was calculated from theequation A=ε×C×1 (C: concentration of polymer, 1: optical path length).

A value obtained by dividing the average value ε4 of an absorptioncoefficient ε2 at a wavelength of 400 nm and an absorption coefficientε3 at a wavelength of 430 nm by an absorption peak absorbance ε1 derivedfrom a benzene ring at a wavelength of 260 nm was taken as spectralstability.

When this value is larger than 20×10⁻⁶, the color b value of a polymeris bad and the color durability thereof is also poor. The spectralstability is preferably 7×10⁻⁶ or less.

Example 1

A polycarbonate was produced as follows. 137 parts by weight of theabove purified bisphenol A (fB) shown in Table 1 and 135 parts by weightof the above purified DPC (cD) shown in Table 2 were fed to a reactorequipped with a stirrer, fractionating column and decompressor andmolten at 180° C. under a nitrogen atmosphere. After dissolution,5.3×10⁻⁵ part by weight of sodium hypophosphite A1 and 5.46×10⁻³ part byweight of tetramethylammonium hydroxide (B1) were added as catalystsshown in Table 4 to carry out a reaction under agitation at a revolutionspeed of 40 rpm for 20 minutes while the formed phenol was distilled offby reducing the inside pressure of the reactor to 13.33 kPa (100 mmHg).After the temperature was raised to 200° C., the pressure was graduallyreduced to 4.000 kPa (30 mmHg) while the phenol was distilled off, andthe reaction was further continued for 20 minutes. By graduallyincreasing the temperature, the reaction was further carried out at 220°C. for 20 minutes and 240° C. for 20 minutes. The temperature of thereaction mixture was raised to 260° C., the reaction was carried out atthe same temperature for 20 minutes, the temperature was further raisedto 270° C., and the reaction was continued by gradually reducing thepressure to 2.666 kPa (20 mmHg) for 10 minutes and at 1.333 kPa (10mmHg) at a revolution speed of 30 rpm. When the viscosity averagemolecular weight became almost 8,000, the revolution speed was changedto 20 rpm and the reaction was continued until the viscosity averagemolecular weight at 270° C. and 66.7 kPa (0.5 mmHg) became almost15,300.

Subsequently, 4.12×10⁻⁴ part by weight of tetrabutylphosphonium2,4,6-trimethylbenzenesulfonate (may be abbreviated as TMBSPhereinafter) was added as a melt viscosity stabilizer was added andstirred at 260° C. and 66.7 kPa (0.5 mmHg) for 10 minutes. Finally, apolycarbonate having a viscosity average molecular weight of 15,400, 85OH terminal groups (eq/ton-polycarbonate) and a melt viscosity stabilityof 0 was obtained.

The results including other physical properties are shown in Table 4.

Comparative Examples 1 to 4

Polycarbonates were obtained in the same manner as in Example 1 exceptthat bisphenol A, DPC, catalysts and melt viscosity stabilizer shown inTable 4 were used. Finally, polycarbonates shown in Table 5 wereobtained. The results including other physical properties are shown inTable 4 and Table 5.

Examples 2 to 14

Polycarbonates were produced in the same manner as in Example 1 exceptthat bisphenol A, DPC, catalysts and melt viscosity stabilizer shown inTable 4 were used. The results are shown in Table 4.

Not described individually, according to the experimental results ofExamples 2 to 14, the number of OH terminal groups was 85±3(eq/ton-polycarbonate) and the melt viscosity stability was 0.

The color of a polycarbonate having a viscosity average molecular weightof 20,000 or less is strictly evaluated by its b value. Therefore, inthe present invention which is aimed to produce a polycarbonate havingexcellent color, when a polymer pellet has a color b value of more than0.1, it is tinted with yellow and therefore judged as unacceptable. Whena polymer pellet has a b value of less than 0.1, it is little tintedwith yellow and therefore judged as acceptable. As understood from theresults, when DPC and bisphenol A whose aldehyde contents were reducedto 0.3 μ-equivalent/bisphenol A and DPC compared with a conventional rawmaterial were used as polymerization raw materials, it was judged thatthe obtained polycarbonate pellet had excellent color with a smallnegative b value and little yellow tint.

Example 15 Comparative Example 5

Polymerization was continued until the viscosity average molecularweight became 22,500 in Example 1 and Comparative Example 2, and 2.1parts by weight of 2-methoxycarbonylphenylphenyl carbonate (maybeabbreviated as SAM hereinafter) was added as a terminal capping agent atthis point and stirred at 260° C. and 133.3 Pa (1 mmHg) for 10 minutes.Thereafter, 5.26×10⁻⁴ part by weight of DBSP was added as a meltviscosity stabilizer and stirred at 260° C. and 66.7 Pa (0.5 mmHg) for10 minutes. Finally, a polycarbonate having a viscosity averagemolecular weight of 22,600, 30 terminal OH groups (eq/ton-polycarbonate)and a melt viscosity stability of 0 and a polycarbonate having aviscosity average molecular weight of 22,500, 32 terminal OH groups(eq/ton-polycarbonate) and a melt viscosity stability of 0 wereobtained.

The results including other physical properties are shown in Table 4.

TABLE 4 Ex. 1 C. Ex. 1 C. Ex. 2 C. Ex. 3 C. Ex. 4 Type of DPC cD GD bDbD cD Type of BPA fB GB dB eB dB Catalyst Alkali metal catalyst type A1A1 A1 A1 A1 amount (× 10⁻⁵ part by weight) 5.3 5.3 5.3 5.3 5.3(μmol/BPA) 1 1 1 1 1 basic compound type B1 B1 B1 B1 B1 amount (× 10⁻³part by weight) 5.46 5.46 5.46 5.46 5.46 (μmol/BPA) 100 100 100 100 100melt viscosity stabilizer type TMBSP TMBSP TMBSP TMBSP TMBSP amount (×10⁻⁴ part by weight) 4.12 4.12 4.12 4.12 4.12 physical propertiesviscosity average molecular weight 15,400 15,300 15,500 15,200 15,200color (pellet L value) 65 64 64 64 64 color (pellet b value) −0.6 2.51.6 0.6 0.6 side reactivity (× 10⁻²) 0.1 or less 2.8 2.2 1.5 2,1 Ex. 2Ex. 3 Ex. 4 Ex. 5 Ex. 6 Type of DPC cD cD cD cD cD Type of BPA eB eB eBeB eB Catalyst Alkali metal catalyst type A1 A2 A3 A4 A6 amount (× 10⁻⁵part by weight) 5.3 1.7 4.9 3.4 1.6 (μmol/BPA) 1 0.7 0.7 0.7 0.7 basiccompound type B1 B3 B4 B4 B5 amount (× 10⁻³ part by weight) 5.46 47.938.9 38.9 10.9 (μmol/BPA) 100 200 200 200 200 melt viscosity stabilizertype TMBSP BSP BSP BSP BSP amount (× 10⁻⁴ part by weight) 4.12 3.74 3.743.74 3.74 physical properties viscosity average molecular weight 15,30015,400 15,300 15,200 15,300 color (pellet L value) 65 65 65 65 65 color(pellet b value) −0.2 −0.4 −0.3 −0.4 −0.3 side reactivity (× 10⁻²) 0.30.2 0.1 0.2 0.2 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Type of DPC cD cD cD cDcD Type of BPA fB fB fB fB fB Catalyst Alkali metal catalyst type A8 A8A8 A8 A6 amount (× 10⁻⁵ part by weight) 4.5 6.3 9 18 1.6 (μmol/BPA) 0.50.7 1.0 2.0 0.7 basic compound type B2 B2 B2 B2 B2 amount (× 10⁻³ partby weight) 7.8 7.8 7.8 7.8 16.5 (μmol/BPA) 50 50 50 50 100 meltviscosity stabilizer type DBSP DBSP DBSP DBSP SABP amount (× 10⁻⁴ partby weight) 2.63 3.68 5.26 10.52 2.58 physical properties viscosityaverage molecular weight 15,200 15,300 15,400 15,300 15,300 color(pellet L value) 64 65 65 64 65 color (pellet b value) −0.5 −0.6 −0.6−0.4 −0.5 side reactivity (× 10⁻²) 0.1 0.1 or less 0.1 or less 0.1 0.1or less Ex. 12 Ex. 13 Ex. 14 Ex. 15 C. Ex. 5 Type of DPC cD cD cD cD bDType of BPA fB fB fB fB dB Catalyst Alkali metal catalyst type A1 A2 A3A1 A1 amount (× 10⁻⁵ part by weight) 3.7 1.7 4.9 5.3 5.3 (μmol/BPA) 0.70.7 0.7 1 1 basic compound type B3 B4 B1 B1 B1 amount (× 10⁻³ part byweight) 23.9 19.4 5.46 5.46 5.46 (μmol/BPA) 100 100 100 100 100 meltviscosity stabilizer type SABP SABP SABP DBSP DBSP amount (× 10⁻⁴ partby weight) 2.58 2.58 2.58 5.26 5.26 physical properties viscosityaverage molecular weight 15,200 15,300 15,400 22,600 22,500 color(pellet L value) 64 65 64 65 64 color (pellet b value) −0.5 −0.5 −0.50.5 1.0 side reactivity (× 10⁻²) 0.1 or less 0.1 or less 0.1 or less 0.11.2 Ex.: Example C. Ex.: Comparative Example

Alkali Metal Catalysts

A1: sodium hypophosphite, A2: sodium hydroxide, A3: sodium phenoxide,A4: sodium acetate, A5: potassium stearate, A6: sodium borohydride, A7:disodium salt of bisphenol A, A8: cesium hydroxide, A9: potassiumhypophosphite, A10: lithium hypophosphite

Basic Compounds

B1: tetramethylammonium hydroxide, B2: tetrabutylphosphonium hydroxide,B3: tetramethylammonium tetraphenyl borate, B4: tetrabutylphosphoniumhypophosphite,

B5: tetrabutylphosphonium hypophosphite, B6: tetramethylammoniumhypophosphite, B7: tetrabutylammonium hypophosphite

Melt Viscosity Stabilizers

DBSP: tetrabutylphosphonium dodecylbenzensulfonate, TMBSP:tetrabutylphosphonium 2,4,6-trimethylbenzenesulfonate, BSP:tetramethylphosphonium benzenesulfonate, SABP:bis(tetrabutylphosphonium) sulfate

TABLE 5 viscosity aver- number of OH melt age molecular terminal groupsviscosity Example weight eq/ton-PC stability C. Ex. 1 15,300 85 0 C. Ex.2 15,500 84 0 C. Ex. 3 15,200 86 0 C. Ex. 4 15,200 85 0 C. Ex.:Comparative Example

Examples 16 to 22

Polycarbonates were obtained in the same manner as in Example 1 exceptthat DPC, bisphenol A, catalysts and melt viscosity stabilizer shown inTable 6 were used. The results are shown in Table 6.

Not described individually, according to the experimental results ofExamples 16 to 22, the number of OH terminal groups was 85±3 (eq/ton-PC)and the melt viscosity stability was 0.

As for the color b value of a polycarbonate having a viscosity averagemolecular weight of 20,000 or less, when DPC and bisphenol A whosealdehyde contents were reduced to 0.3 μ-equivalent/bisphenol A and DPCwere used as polymerization raw materials and a hypophosphorous acidcompound was used as a polymerization catalyst, it was judged that theobtained polycarbonate pellets had a much improved b value and weresuitable for optical applications which require transparency and strictcolor compared with polycarbonate pellets obtained from conventional rawmaterials as understood from the results of Table 5. It is easilyunderstood that when bisphenol A treated with a hypophosphorous acidcompound is used, a more excellent color is provided.

When the polycarbonate having excellent color is used for opticalapplication, its excellent color is developed more advantageously.

Examples 23 and 24

Polymerization was continued until the viscosity average molecularweight became 22,500 in the same manner as in Except 1 except that DPC,bisphenol A, catalysts and melt viscosity stabilizer shown in Table 6were used. 2.1 parts by weight of 2-methoxycarbonylphenylphenylcarbonate (may be abbreviated as SAM hereinafter) was added as aterminal capping agent at this point and stirred at 260° C. and 133.3 Pa(1 mmHg) for 10 minutes. Thereafter, 5.26×10⁻⁴ part by weight of DBSPwas added as a melt viscosity stabilizer and stirred at 260° C. and 66.7Pa (0.5 mmHg) for 10 minutes. Finally, a polycarbonate having aviscosity average molecular weight of 22,500, 30 terminal OH groups(eq/ton-polycarbonate) and a melt viscosity stability of 0 and apolycarbonate having a viscosity average molecular weight of 22,600, 32terminal OH groups (eq/ton-polycarbonate) and a melt viscosity stabilityof 0 were obtained.

The results including other physical properties are shown in Table 6.

TABLE 6 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20 Type of DPC cD cD cD cD cDType of BPA fB fB fB fB fB Catalyst Alkali metal catalyst type A8 A9 A10A9 A10 amount (× 10⁻⁵ part by weight) 6.3 3.1 4.3 4.4 4.4 (μmol/BPA) 0.70.5 1 0.7 1 basic compound type B2 TBAH B2 B5 B6 amount (× 10⁻³ part byweight) 7.8 12.4 24.8 19.4 13.8 (μmol/BPA) 50 80 150 100 100 meltviscosity stabilizer type DBSP DBSP DBSP DBSP DBSP amount (× 10⁻⁴ partby weight) 3.68 2.5 5.3 3.7 5.3 physical properties viscosity averagemolecular weight 13,200 15,400 15,300 15,500 15,400 color (pellet Lvalue) 65 65 65 65 64 color (pellet b value) −0.6 −0.9 −0.9 −0.9 −0.9side reactivity (× 10⁻²) 0.1 or less 0.1 or less 0.1 or less 0.1 or less0.1 or less Ex. 21 Ex. 22 Ex. 23 Ex. 24 Type of DPC cD cD cD cD Type ofBPA fB* fB** fB** fB Catalyst Alkali metal catalyst type A1 A1 A1 A2amount (× 10⁻⁵ part by weight) 5.3 5.3 5.3 2.4 (μmol/BPA) 1 1 1 1 basiccompound type B6 B7 B6 B1 amount (× 10⁻³ part by weight) 13.8 18.4 13.85.5 (μmol/BPA) 100 100 100 100 melt viscosity stabilizer type DBSP DBSPDBSP DBSP amount (× 10⁻⁴ part by weight) 5.3 5.3 5.3 5.3 physicalproperties viscosity average molecular weight 15,300 15,500 22,50022,600 color (pellet L value) 65 65 65 64 color (pellet b value) −1.0−1.1 −0.3 0.4 side reactivity (× 10⁻²) 0.1 or less 0.1 or less 0.1 orless 0.3 Ex.: Example

Examples 25 to 28

Polycarbonates were produced in the same manner as in Example 1 exceptthat DPC, bisphenol A, bisphenol A prills, catalysts and melt viscositystabilizer shown in Table 7 were used. The results are shown in Table 7.

Not described individually, according to the experimental results ofExamples 25 to 28, the number of OH terminal groups was 85±3 (eq/ton-PC)and the melt viscosity stability was 0.

As understood from the experimental results, when bisphenol A prillshaving a particle diameter of 0.2 to 3 mm, a specific surface area of0.05 to 0.2 g/m², a pore surface area of 0.01 to 0.1 ml/g and a color bvalue of 2 or more were used, a polycarbonate having a viscosity averagemolecular weight of 20,000 or less, which could meet very strict polymercolor requirements, was advantageously obtained.

It was further discovered that the color durability of a polycarbonatepellet could be advantageously improved by using the bisphenol A prillsof the present invention.

Since a pellet may be kept for a long time and its color change maybecome a subject of discussion, the improvement of color durability isof great significance.

Examples 29 to 31

A polymerization reaction was continued until the viscosity averagemolecular weight became 22,500 in the same manner as in Example 1 exceptthat DPC, bisphenol A, bisphenol A prills and catalysts shown in Table 7were used. At this point, 2.1 parts by weight of SAM was added as aterminal capping agent and stirred at 260° C. and 133.3 Pa (1 mmHg) for10 minutes. Thereafter, 5.26×10⁻⁴ part by weight of DBSP was added as amelt viscosity stabilizer and stirred at 260° C. and 66.7 Pa (0.5 mmHg)for 10 minuets. Finally, a polycarbonate having a viscosity averagemolecular weight of 22,500, 30 terminal OH groups (eq/ton-polycarbonate)and a melt viscosity stability of 0, a polycarbonate having a viscosityaverage molecular weight of 22,400, 32 terminal OH groups(eq/ton-polycarbonate) and a melt viscosity stability of 0, and apolycarbonate having a viscosity average molecular weight of 22,500, 30terminal OH groups (eq/ton-polycarbonate) and a melt viscosity stabilityof 0 were obtained.

The results including other physical properties are shown in Table 7.

TABLE 7 Ex. 25 Ex. 26 Ex. 27 Type of DPC cD cD cD Type of BPA fB-b fB-bfB-b Catalyst Alkali metal catalyst type A7 A7 A7 amount (× 10⁻⁵ part byweight) 8.2 8.2 8.2 (μmol/BPA) 1 1 1 basic compound type B1 B1 B1 amount(× 10⁻³ part by weight) 5.46 5.46 5.46 (μmol/BPA) 100 100 100 meltviscosity stabilizer type DBSP DBSP DBSP physical properties amount (×10⁻⁴ part by weight) 5.26 5.26 5.26 viscosity average molecular 15,30015,200 15,400 weight color (pellet L value) 65 65 65 color (pellet bvalue) −0.9 −1.0 −1.0 side reactivity (× 10⁻²) 0.1 or less 0.1 or less0.1 or less color durability of pellet Δb 0.5 0.5 0.4 ΔbMax-Min 0.4 0.40.4 spectral stability (× 10⁻⁶) 4 3 3 Ex. 28 Ex. 29 Ex. 30 Ex. 31 Typeof DPC cD cD cD cD Type of BPA fB-c fB fB-a fB-b Catalyst Alkali metalcatalyst type A7 A1 A1 A1 amount (× 10⁻⁵ 8.2 5.3 5.3 5.3 part by weight)(μmol/BPA) 1 1 1 1 basic compound type B1 B1 B1 B1 amount (× 10⁻³ 5.466.46 6.46 6.46 part by weight) (μmol/BPA) 100 100 100 100 melt viscositystabilizer type DBSP DBSP DBSP DBSP amount (× 10⁻⁴ 5.26 5.26 5.26 5.26part by weight) physical properties viscosity average 15,300 22,50022,400 22,500 molecular weight color (pellet L value) 65 65 65 65 color(pellet b value) −0.7 0.5 −0.1 −0.1 side reactivity (× 10⁻²) 0.1 or less0.2 0.1 or less 0.1 or less color durability of pellet Δb 0.7 1 0.4 0.5ΔbMax-Min 1.1 1.2 0.5 0.5 spectral stability (× 10⁻⁶ ) 8 9 3 3 Ex.:Example

Evaluation of Disk Moldability

Example 32 Comparative Example 6

0.01 wt % of tris(2,4,6-di-tert-butylphenyl)phosphite and 0.08 wt % ofglycerol monostearate were added to the polycarbonates obtained inExample 1 and Comparative Example 1. Then, the obtained compositionswere melt kneaded and pelletized by a vented double-screw extruder(KTX-46 of Kobe Steel Co., Ltd.) while they were devolatilized at acylinder temperature of 240° C. The pellets were used to mold DVD(DVD-Video) disk substrates and a temperature and humidity deteriorationtest was made on these substrates.

A DVD mold was set in the DISK3 M III injection molding machine ofSumitomo Heavy Industries, Ltd., a nickel DVD stamper which storedinformation such as an address signal was attached to this mold, theabove pellets were supplied into the hopper of the molding machineautomatically, and DVD disk substrates having a diameter of 120 mm and athickness of 0.6 mm were molded at a cylinder temperature of 380° C., amold temperature of 115° C., an injection rate of 200 mm/sec and aholding pressure of 3,432 kPa (35 kgf/cm²).

To test the long-term reliability of each optical disk under extremetemperature and humidity conditions, the aromatic polycarbonate opticaldisk substrates were kept at a temperature of 80° C. and a relativehumidity of 85% for 1,000 hours and measured for the following items forevaluation.

number of white points per disk: The optical disk substrates after thetemperature and humidity deterioration test were observed through apolarization microscope to count white points having a length of 10 μmor more. This was made on 25 optical disk substrates to obtain anaverage number of white points per disk and taken as the number of whitepoints.

As a result, the number of white points was 0.1 per disk in Example 16and 4.6 per disk in Comparative Example 6. Therefore, it is understoodthat the polycarbonate of the present invention has excellent stability.

Reference Examples 1 and 2 (Production Examples of Polycarbonate byInterfacial Polymerization)

502.8 g (2.21 mols) of bisphenol A (Reference Example 1) or bisphenol Aprills (fB-a; Reference Example 2), 2.21 l (4.19 mols of sodiumhydroxide) of a 7.2% aqueous solution of sodium hydroxide and 0.98 g(0.0056 mol) of sodium hydrosulfite were fed as raw materials to a5-liter reactor equipped with a phosgene blow-in tube, thermometer andstirrer and dissolved, 1.27 l of methylene chloride and a 48.5% aqueoussolution of sodium hydroxide (0.98 mol of sodium hydroxide) were addedunder agitation, and 250.80 g (0.253 mol) of phosgene were added at 25°C. in 180 minutes to carry out a phosgenation reaction.

After the end of phosgenation, 17.51 g (0.117 mol) ofp-tert-butylphenol, 80.40 g (0.97 mol of sodium hydroxide) of a 48.5%aqueous solution of sodium hydroxide and 1.81 ml (0.013 mol) oftriethylamine as a catalyst were added, kept at 33° C. and stirred for 2hours to terminate the reaction. A methylene chloride layer wasseparated from the reaction mixture which was then washed with water 10times to be purified until sodium chloride was not detected in order toobtain a polycarbonate having a viscosity average molecular weight of15,300. 0.01 wt % of tris(2,4-di-tert-butylphenyl)phosphite and 0.08 wt% of glycerol monostearate were added to and kneaded with the obtainedpolycarbonate by a double-screw extruder and pelletized.

The obtained polycarbonate pellet of Reference Example 1 had a color bvalue of 1.1 whereas the obtained polycarbonate pellet of ReferenceExample 2 had an excellent color b value of −0.4.

Example 33

The aromatic polycarbonate of the above Example 15 was kept molten afterpolymerization and supplied into the T die of a molding machinequantitatively by a gear pump to be extrusion molded. 0.003 wt % ofbis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite was added beforethe gear pump and the resulting mixture was molded into a sheet having athickness of 2 mm or 0.2 mm and a width of 800 mm by sandwiching betweenmirror cooling rolls or touching one side.

A visible light curable plastic adhesive (BENEFIX PC of Ardel Co., Ltd.)was applied to one side of the obtained aromatic polycarbonate sheet(thickness of 2 mm) and two of the sheet were extruded and assembledtogether such that air bubbles were not contained between the sheets.After assembly, the resulting laminate was exposed to 5,000 mJ/cm² lightfrom a light curing device equipped with a metal halide lamp forirradiating visible light to cure the adhesive layer.

When the bonding strength of the obtained laminated sheet was measuredin accordance with JIS K-6852 (method for testing the compression shearstrength of an adhesive), it was 9.92 MPa (101 kgf/cm²).

A uniform mixture of ink (Natsuda 70-9132: 136D smoke color) and asolvent (isophorone/cyclohexane/isobutanol=40/40/20 (wt %)) was printedon the 0.2 mm-thick aromatic polycarbonate sheet by a silk screenprinter and dried at 100° C. for 60 minutes. The printed ink surface waswell printed without a transfer failure.

Separately, 30 parts by weight of a polycarbonate resin (specificviscosity of 0.895, Tg of 175° C.) obtained by carrying out a generalinterfacial polycondensation reaction between1,1-bis(4-hydroxyphenyl)cyclohexane and phosgene, 15 parts of Plast Red8370 (of Arimoto Kagaku Kogyo Co., Ltd.) as a dye and 130 part ofdioxane as a solvent were uniformaly mixed together to obtain printingink. A sheet (thickness: 0.2 mm) printed with the above printing ink wasset in an injection mold and insert molding was carried out using apolycarbonate resin pellet (Panlite L-1225 of Teijin Kasei Co., Ltd.) at310° C. The printed portion of the obtained insert molded article had noabnormalities such as bleeding and blurring in pattern and had a goodappearance.

Examples 34 to 40

The aromatic polycarbonate of the above Example 30 was kept molten afterpolymerization and supplied into the extruder by a gear pump. 0.003 wt %of tris(2,4-di-tert-butylphenyl)phosphite and 0.05 wt % of trimethylphosphate were added before the extruder to obtain an aromaticpolycarbonate pellet.

The pellet and components shown in Tables 8 and 9 were uniformly mixedtogether by a tumbler and the resulting mixture was pelletized by a 30mm-diameter vented double-screw extruder (KTX-30 of Kobe Steel Co.,Ltd.) at a cylinder temperature of 260° C. and a vent pressure of 1.33kPa (10 mmHg) while it was degassed. The obtained pellet was dried at120° C. for 5 hours and molded into a test sample for measurement at acylinder temperature of 270° C. and a mold temperature of 80° C. by ainjection molding machine (SG150U of Sumitomo Heavy Industries, Ltd.).The evaluation results are shown in Tables 8 and 9.

TABLE 8 Ex. 34 Ex. 35 Ex. 36 Ex. 37 Composition Polycarbonate of wt % 6060 60 60 Example 30 ABS wt % 40 40 40 — AS wt % — — — 30 MBS wt % — — —10 Total wt 100 100 100 100 G wt 15 — — 15 W wt — 15 — — T wt — — 15 —WAX wt — 1 1 — Characteristic properties Flexural modulus MPa 3,4503,200 2,850 3,350 Fluidity cm 30 29 30 36 Notched impact value J/m 70 7555 85 Ex.: Example wt: part by weight

TABLE 9 Ex. 38 Ex. 39 Ex. 40 Composition Polycarbonate of Example 30 wt% 70 70 + PBT wt % 30 5 PET wt % 30 25 Total wt % 100 100 100 E-1 5 5E-2 wt 5 G wt 20 W wt 10 T wt 10 WAX wt 1 1 Characteristic propertiesFlexural modulus MPa 5,800 3,600 3,450 Chemical resistance % 88 86 84Notched impact value J/m 220 550 510 Ex.: Example wt: part by weight

(1)-1 ABS: styrene-butadiene-acrylonitrile copolymer; Suntac UT-61;Mitsui Chemicals, Inc.

(1)-2 AS; styrene-acrylonitrile copolymer; Stylac-AS 767 R27; AsahiChemical Industry, Co., Ltd.

(1)-3 PET: polyethylene terephthalate; TR-8580; Teijin Limited,intrinsic viscosity of 0.8

(1)-4 PBT: polybutylene terephthalate; TRB-H; Teijin Limited, intrinsicviscosity of 1.07

(2)-1 MBS: methyl (meth)acrylate-butadiene-styrene copolymer; KaneaceB-56; Kaneka Corporation

(2)-2 E-1: butadiene-alkyl acrylate-alkyl methacrylate copolymer;Paraloid EXL-2602; Kureha Chemical Industry, Co., Ltd.

(2)-3 E-2: composite rubber having a network structure that apolyorganosiloxane component and a polyalkyl (meth)acrylate rubbercomponent penetrate into each other; Metabrene S-2001; Mitsubishi RayonCo., Ltd.

(3)-1 T: talc; HS-T0.8; Hayashi Kasei Co., Ltd., average particlediameter L of 5 μm measured by laser diffraction method, L/D of 8

(3)-2 G: glass fiber; chopped strand ECS-03T-511; Nippon Electric GlassCo., Ltd., urethane bundling, fiber diameter of 13 μm

(3)-3 W: wollastonite; Saikatec NN-4; Tomoe Kogyo Co., Ltd., numberaverage fiber diameter D obtained by observation through electronmicroscope of 1.5 μm, average fiber length of 17 μm, aspect ratio L/D of20

(4) WAX: olefin-based wax obtained by copolymerizing α-olefin and maleicanhydride; Diacalna P30; Mitsubishi Kasei Co., Ltd. (maleic anhydridecontent of 10 wt %)

(A) Flexural Modulus

The flexural modulus was measured in accordance with ASTM D790.

(B) Notched Impact Value

The impact value was measured by colliding a weight with a 3.2 mm thicktest sample from the notch side in accordance with ASTM D256.

(C) Fluidity

The fluidity was measured by an Archimedes type spiral flow (thicknessof 2 mm, width of 8 mm) at a cylinder temperature of 250° C., a moldtemperature of 80° C. and an injection pressure of 98.1 MPa.

(D) Chemical Resistance

1% strain was provided to a tensile test piece used in ASTM D638 whichwas then immersed in Esso regular gasoline heated at 30° C. for 3minutes to measure the tensile strength and calculate the tensilestrength retention of the test piece. The retention was calculated fromthe following equation.

retention (%)=(strength of treated sample/strength of untreatedsample)×100

What is claimed is:
 1. A process for producing a polycarbonate by meltpolycondensing a dihydroxy compound and a carbonic acid diester in thepresence of an ester exchange catalyst, wherein a raw material whichcontains a dihydroxy compound represented by the following formula (1):

wherein R¹ and R² are each independently an alkyl group having 1 to 20carbon atoms, alkoxy group having 1 to 20 carbon atoms, cycloalkyl grouphaving 6 to 20 carbon atoms, aryl group having 6 to 20 carbon atoms,cycloalkoxy group having 6 to 20 carbon atoms or aryloxy group having 6to 20 carbon atoms, m and n are each independently an integer of 0 to 4,and X is a single bond, oxygen atom, carbonyl group, alkylene grouphaving 1 to 20 carbon atoms, alkylidene group having 2 to 20 carbonatoms, cycloalkylene group having 6 to 20 carbon atoms, cycloalkylidenegroup having 6 to 20 carbon atoms, arylene group having 6 to 20 carbonatoms or a group having 6 to 20 carbon atoms, and an aldehyde compoundin an amount of no more than 3×10⁻⁶ equivalent in terms of an aldehydegroup based on 1 mol of the dihydroxy compound represented by the aboveformula (1) is used as one raw material comprising the above dihydroxycompound and a raw material which contains a carbonic acid diester andan aldehyde compound in an amount of no more than 3×10⁻⁶ equivalent interms of an aldehyde group based on 1 mol of the carbonic acid diesteris used as the other raw material comprising the above carbonic aciddiester.
 2. The process of claim 1, wherein the one raw materialcontains an aldehyde compound in an amount of no more than 2×10⁻⁶equivalent in terms of an aldehyde group based on 1 mol of the dihydroxycompound represented by the above formula (1).
 3. The process of claim1, wherein the other raw material contains an aldehyde compound in anamount of no more than 2×10⁻⁶ equivalent in terms of an aldehyde groupbased on 1 mol of the carbonic acid diester.
 4. The process of claim 1,wherein a combination of the one raw material and the other raw materialcontains an aldehyde compound in an amount of no more than 3×10⁻⁶equivalent in terms of an aldehyde group based on 1 mol of the dihydroxycompound represented by the above formula (1).
 5. The process of claim1, wherein the aldehyde compound is an impurity contained in the one rawmaterial and the other raw material.
 6. The process of claim 1, whereinthe one raw material contains a carboxylic acid compound in an amount ofno more than 3×10⁻⁶ equivalent in terms of a carboxyl group based on 1mol of the dihydroxy compound represented by the above formula (1). 7.The process of claim 1, wherein the other raw material contains acarboxylic acid compound in an amount of no more than 3×10⁻⁶ equivalentin terms of a carboxyl group based on 1 mol of the carbonic aciddiester.
 8. The process of claim 1, wherein the one raw material is inthe form of globular particles which include particles having a diameterof 0.1 to 3 mm in an amount of 70 wt % or more and have a specificsurface area of 0.05 to 0.2 m²/g and a pore volume of 0.01 to 0.1 ml/g.9. The process of claim 8, wherein the color L and b values of theglobular particles are 80 or more and 2 or less, respectively.
 10. Theprocess of claim 1, wherein the ester exchange catalyst is a combinationof a) at least one basic compound selected from the group consisting ofa nitrogen-containing basic compound and a phosphorus-containing basiccompound and b) at least one metal compound selected from the groupconsisting of an alkali metal compound and an alkali earth metalcompound.
 11. The process of claim 10, wherein the basic compound isused in an amount of 1×10⁻⁵ to 1×10⁻³ equivalent based on 1 mol of thedihydroxy compound.
 12. The process of claim 10, wherein the metalcompound is used in an amount of 5×10⁻⁸ to 5×10⁻⁶ equivalent based on 1mol of the dihydroxy compound.
 13. The process of claim 10, wherein thealkali metal compound is an alkali metal hypophosphite and the alkaliearth metal compound is an alkali earth metal hypophosphite.
 14. Anaromatic polycarbonate pellet which comprises an aromatic polycarbonatecomposed mainly of a recurring unit represented by the following formula(2):

wherein R¹ and R² are each independently an alkyl group having 1 to 20carbon atoms, alkoxy group having 1 to 20 carbon atoms, cycloalkyl grouphaving 6 to 20 carbon atoms, aryl group having 6 to 20 carbon atoms,cycloalkoxy group having 6 to 20 carbon atoms or aryloxy group having 6to 20 carbon atoms, m and n are each independently an integer of 0 to 4,and X is a single bond, oxygen atom, carbonyl group, alkylene grouphaving 1 to 20 carbon atoms, alkylidene group having 2 to 20 carbonatoms, cycloalkylene group having 6 to 20 carbon atoms, cycloalkylidenegroup having 6 to 20 carbon atoms, arylene group having 6 to 20 carbonatoms or alkylene-arylene-alkylene group having 6 to 20 carbon atoms,and having a viscosity average molecular weight of 10,000 to 17,000 anda value of 1×10⁻⁶ to 20×10⁻⁶ obtained by dividing an average value ofabsorbance at a wavelength of 400 nm and absorbance at a wavelength of430 nm by absorbance at a wavelength of 260 nm, and which has a b valuemeasured in accordance with JIS K7105 of −1.0 to 0.0.
 15. The pellet ofclaim 14 which has a b value of −0.5 to 0.0.
 16. A method for producingan optical disk substrate, which comprises forming an optical disksubstrate from a pellet of claim 14.